Pytheas observes the rhythm of the tides which is that of the moon: he loses fifty-four minutes each day. On his return to Massalia, few scientists will believe him. Once again, he is taken for a liar!
Since he has been in the Ocean, Pytheas has encountered a phenomenon that was unknown to him in the Mediterranean. He describes it in detail when he describes the Cassiterides Islands. And the further north he goes, the more important the phenomenon is. These are the tides.
For us, Mediterraneans, whatever we know about it, it is always with surprise when we discover this phenomenon. Can we imagine that it is Pytheas's? The Bretons and the British with whom he has contacts know the phenomenon well and give him its main characteristics. The movement of the tides is in conjunction with the moon. When the moon is in quarter, the tides are of low amplitude. On the other hand, when the moon is in phase or in opposition with the sun, it is the period of high tides, and particularly at the equinoxes. Pytheas does not need anyone to realize that the sea rises and falls twice a day, at the rhythm of the moon which loses fifty-four minutes per day.
 |
Massaliotes amphorae. Massalia has developed its own amphora shapes.
|
Pliny writes, quoting Pytheas: "Why the tides of the sea rise and fall and where extraordinary tides take place" (D11). and then, "above Britannia a tidal swell eighty cubits high" (D12-1). Which is about twenty-five meters. He may not have observed such amplitudes himself, but they are certainly reported to him. Is this a possible height? Why not, during the high equinox tides, if a strong depression is present, and in addition, and this is frequently the case, a storm arises, the water can rise very high. Note that Strabo is a little confused: "having learned from them that at the summer solstice the tides in both directions, both the falling and the rising, have their maximum amplitude" (D12). It is at the equinoxes that the tides are the strongest.
Pytheas explanation of the tides will help to elucidate the mystery of the currents of the Strait of Messina, between Italy and Sicily (D10). Pytheas is the first to give an explanation to the Mediterranean world. Which earns him the ire of the Greek world. The sea cannot rise that high, and if its level changes it is due to the rivers. As for the action of the moon, he is considered a fabulist.